FePt-C-based sputtering target and process for producing the same

ABSTRACT

An FePt—C-based sputtering target contains Fe, Pt, and C and has a structure in which an FePt-based alloy phase and a C phase containing unavoidable impurities are mutually dispersed, the FePt-based alloy phase containing Pt in an amount of 40 at % or more and 60 at % or less with the balance being Fe and unavoidable impurities. The content of C is 21 at % or more and 70 at % or less based on the total amount of the target.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 14/008,211,filed Sep. 27, 2013, the entire content of which is incorporated hereinby reference.

TECHNICAL FIELD

The present invention relates to a FePt—C-based sputtering target and toa process for producing the same.

BACKGROUND ART

A FePt alloy can be provided with the fct (Ordered Face CenteredTetragonal) structure which has high crystal magnetic anisotropy byheat-treating at an elevated temperature (for example, at 600° C. orhigher), and therefore a FePt alloy has been highlighted as a magneticrecording medium. To make FePt particles smaller and more uniform in thethin film of the FePt alloy, it is proposed that a predeterminedquantity of carbon (C) be included into the thin film of the FePt alloy(for example, Patent Literature 1).

However, the formation method of the FePtC thin film, described in thePatent Literature 1, is the method of vapor-depositing Fe, Pt, and Csimultaneously on a MgO (100) board by using the Fe target of a 2-inchdiameter, C target of a 2-inch diameter, and the Pt target of 5 mm inheight and width. In this method, it is difficult to obtain the filmwhose composition is controlled strictly. Additionally, three targetsare required and each target needs a cathode, a power supply, etc, andso the cost of equipment becomes high while the preparatory work ofsputtering takes time and effort.

On the other hand, the technology for producing the sputtering targetconsisting of a PtFe system alloy according to a casting process isdescribed in the Patent Literature 2. And in claim 2, 3 and theparagraph 0017 of a Patent Literature 2, C is raised as one choice inthe many choice of the element added into a PtFe-based alloy.

However, C is only raised as one of the many choices of the elementadded into a PtFe-based alloy, and the specific working example in whichC is actually added into the PtFe-based alloy is not shown. Even if Ccan be added into a PtFe-based alloy in the technology described in thePatent Literature 2, the content of carbon (C) in a FePt—C sputteringtarget is 20 at % at the maximum as described in claim 2, 3 and theparagraph 0017 of a Patent Literature 2.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent No. 3950838-   Patent Literature 2: Japanese Patent Application Laid-Open No.    2006-161082

SUMMARY OF INVENTION Technical Problem

The present invention has been made in view of the aforementionedproblems. It is an object of the present invention to provide anFePt—C-based sputtering target which enables an FePtC-based thin filmcontaining a large amount of carbon to be formed from a single targetwithout using a plurality of targets, and to provide a process forproducing the FePt—C-based sputtering target.

Solution to Problem

As a result of intensive research to solve the aforementioned problem,the present inventors found out that the aforementioned problem issolvable with the following FePt—C-based sputtering targets and solvablewith the following processes for producing the FePt—C-based sputteringtarget, and the present inventors created the present invention.

Namely, a first aspect of an FePt—C-based sputtering target according tothe present invention is an FePt—C-based sputtering target containingFe, Pt, and C, wherein the FePt—C-based sputtering target has astructure in which an FePt-based alloy phase and a C phase containingunavoidable impurities are mutually dispersed, the FePt-based alloyphase containing Pt in an amount of 40 at % or more and 60 at % or lesswith the balance being Fe and unavoidable impurities, and wherein C iscontained in an amount of 21 at % or more and 70 at % or less based onthe total amount of the target.

The phrase “an FePt-based alloy phase and a C phase containingunavoidable impurities are mutually dispersed” is a concept including astate in which the FePt-based alloy phase is a dispersion medium and theC phase is a dispersoid and a state in which the C phase is a dispersionmedium and the FePt-based alloy phase is a dispersoid and furtherincluding a state in which the FePt-based alloy phase and the C phaseare mutually mixed but it is not possible to determine which phase is adispersion medium and which phase is a dispersoid.

In the present description, the term “FePt-based alloy” means an alloycontaining Fe and Pt as main components and is meant to include not onlybinary alloys containing only Fe and Pt but also ternary and higheralloys containing Fe and Pt as main components and further containing ametal element other than Fe and Pt. The term “FePt—C-based sputteringtarget” means a sputtering target containing Fe, Pt, and C as maincomponents. The term “FePtC-based thin film” means a thin filmcontaining Fe, Pt, and C as main components.

A second aspect of an FePt—C-based sputtering target according to thepresent invention is an FePt—C-based sputtering target containing Fe,Pt, and C and further containing one or more kinds of metal elementsother than Fe and Pt, wherein the FePt—C-based sputtering target has astructure in which an FePt-based alloy phase and a C phase containingunavoidable impurities are mutually dispersed, the FePt-based alloyphase containing Pt in an amount of 40 at % or more and less than 60 at% and the one or more kinds of metal elements other than Fe and Pt in anamount of more than 0 at % and 20 at % or less with the balance being Feand unavoidable impurities and with the total amount of Pt and the oneor more kinds of metal elements being 60 at % or less, and wherein C iscontained in an amount of 21 at % or more and 70 at % or less based onthe total amount of the target.

In the second aspect of the FePt—C-based sputtering target according tothe present invention, the one or more metal elements other than Fe andPt may be one or more kinds of Cu, Ag, Mn, Ni, Co, Pd, Cr, V, and B. Theone or more metal elements other than Fe and Pt may include Cu, or theone or more metal elements other than Fe and Pt may be only Cu.

Preferably, the C phase has an average phase size of 0.6 μm or less asdetermined by an intercept method.

A method for determining the average size of the C phase by theintercept method will be described later in

DESCRIPTION OF EMBODIMENTS

Preferably, the FePt—C-based sputtering target has a relative density of90% or higher.

Preferably, the content of oxygen is 100 mass ppm or less based on thetotal mass of the target. Preferably, the content of nitrogen is 30 massppm or less based on the total mass of the target.

Some of the above-described FePt—C-based sputtering targets can bepreferably used for a magnetic recording medium.

A first aspect of a process for producing an FePt—C-based sputteringtarget according to the present invention is a process for producing anFePt—C-based sputtering target, including: adding C powder containingunavoidable impurities to FePt-based alloy powder containing Pt in anamount of 40 at % or more and 60 at % or less with the balance being Feand unavoidable impurities; mixing the C powder and the FePt-based alloypowder in an atmosphere containing oxygen to produce a powder mixture;and then molding the produced powder mixture while the powder mixture isheated under pressure.

And, a second aspect of a process for producing an FePt—C-basedsputtering target according to the present invention is a process forproducing an FePt—C-based sputtering target, including: adding C powdercontaining unavoidable impurities to FePt-based alloy powder containingPt in an amount of 40 at % or more and less than 60 at % and one or morekinds of metal elements other than Fe and Pt in an amount of more than 0at % and 20 at % or less with the balance being Fe and unavoidableimpurities and with the total amount of Pt and the one or more kinds ofmetal elements being 60 at % or less; mixing the C powder and theFePt-based alloy powder in an atmosphere containing oxygen to produce apowder mixture; and then molding the produced powder mixture while thepowder mixture is heated under pressure.

In the second aspect of the process for producing an FePt—C-basedsputtering target according to the present invention, the one or moremetal elements other than Fe and Pt may be one or more kinds of Cu, Ag,Mn, Ni, Co, Pd, Cr, V, and B. The one or more metal elements other thanFe and Pt may include Cu, or the one or more metal elements other thanFe and Pt may be only Cu.

The C powder may be added such that the content of C is, for example, 21at % or more and 70 at % or less based on the total amount of the powdermixture.

Preferably, oxygen is supplied to the atmosphere from outside of theatmosphere. This can prevent a shortage of oxygen in the atmosphere andcan suppress ignition of the C powder.

The oxygen may be supplied by supplying air. The use of air as thesupply source of oxygen can reduce cost.

The atmosphere may be air. When the atmosphere is air, the cost can bereduced.

The atmosphere may not be air but may be an atmosphere composedsubstantially of an inert gas and oxygen. In this case, incorporation ofimpurities other than oxygen into the powder mixture during the mixingcan be suppressed.

The concentration of oxygen in the atmosphere may be, for example, 10vol % or higher and 30 vol % or lower.

The atmosphere may be released into the air during the mixing. In thiscase, even when the atmosphere is short of oxygen during the mixing,oxygen can be introduced from the air by releasing the atmosphere intothe air, so that the shortage of oxygen can be mitigated.

Preferably, the C phase in the obtained FePt—C-based sputtering targethas an average phase size of 0.6 μm or less as determined by anintercept method.

Preferably, an atmosphere when the powder mixture is molded while heatedunder pressure is a vacuum or an inert gas atmosphere. In this manner,the amount of impurities such as oxygen in the obtained sintered productcan be reduced.

Preferably, the content of oxygen in the obtained FePt—C-basedsputtering target is 100 mass ppm or less. Preferably, the content ofnitrogen in the obtained FePt—C-based sputtering target is 30 mass ppmor less.

Preferably, the FePt-based alloy powder is produced by an atomizingmethod, in terms of a reduction in the amount of impurities mixed.Preferably, the atomizing method is performed using argon gas ornitrogen gas, in terms of a further reduction in the amount ofimpurities mixed.

Some of the obtained FePt—C-based sputtering targets can be preferablyused for a magnetic recording medium.

A third aspect of the FePt—C-based sputtering target according to thepresent invention is an FePt—C-based sputtering target produced by anyone of the above production processes.

Advantageous Effects of Invention

An FePt—C-based thin film with a high carbon content can be formed byusing the FePt—C-based sputtering target according to the presentinvention alone, i.e., by using only this target without using aplurality of targets.

In the process for producing an FePt—C-based sputtering target accordingto the present invention, the FePt-based alloy powder and the C powderare mixed in an atmosphere containing oxygen to produce a powdermixture. Therefore, the FePt—C-based sputtering target can be producedstably with ignition of the C powder being suppressed. Since Fe and Ptare alloyed, ignition of Fe during mixing with the C powder can also besuppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a low-magnification scanning electron micrograph (an imagetaken at a magnification of 3,000×) of the structure of a sinteredproduct in Example 1 (the cumulative number of ball mill revolutions:4,136,400, sintering temperature: 1,460° C.) (a bar scale in thephotograph: 1 μm).

FIG. 2 is a medium-magnification scanning electron micrograph (an imagetaken at a magnification of 5,000×) of the structure of a sinteredproduct in Example 1 (the cumulative number of ball mill revolutions:4,136,400, sintering temperature: 1,460° C.) (a bar scale in thephotograph: 1 μm).

FIG. 3 is a high-magnification scanning electron micrograph (an imagetaken at a magnification of 10,000×) of the structure of a sinteredproduct in Example 1 (the cumulative number of ball mill revolutions:4,136,400, sintering temperature: 1,460° C.) (a bar scale in thephotograph: 1 μm).

FIG. 4 is a low-magnification scanning electron micrograph (an imagetaken at a magnification of 3,000×) of the structure of a sinteredproduct in Example 2 (the cumulative number of ball mill revolutions:4,073,760, sintering temperature: 1,340° C.) (a bar scale in thephotograph: 1 μm).

FIG. 5 is a medium-magnification scanning electron micrograph (an imagetaken at a magnification of 5,000×) of the structure of a sinteredproduct in Example 2 (the cumulative number of ball mill revolutions:4,073,760, sintering temperature: 1,340° C.) (a bar scale in thephotograph: 1 μm).

FIG. 6 is a high-magnification scanning electron micrograph (an imagetaken at a magnification of 10,000×) of the structure of a sinteredproduct in Example 2 (the cumulative number of ball mill revolutions:4,073,760, sintering temperature: 1,340° C.) (a bar scale in thephotograph: 1 μm).

FIG. 7 is a low-magnification scanning electron micrograph (an imagetaken at a magnification of 3,000×) of the structure of a sinteredproduct in Example 3 (the cumulative number of ball mill revolutions:3,181,680, sintering temperature: 1,300° C.) (a bar scale in thephotograph: 1 μm).

FIG. 8 is a medium-magnification scanning electron micrograph (an imagetaken at a magnification of 5,000×) of the structure of a sinteredproduct in Example 3 (the cumulative number of ball mill revolutions:3,181,680, sintering temperature: 1,300° C.) (a bar scale in thephotograph: 1 μm).

FIG. 9 is a high-magnification scanning electron micrograph (an imagetaken at a magnification of 10,000×) of the structure of a sinteredproduct in Example 3 (the cumulative number of ball mill revolutions:3,181,680, sintering temperature: 1,300° C.) (a bar scale in thephotograph: 1 μm).

FIG. 10 is a low-magnification scanning electron micrograph (an imagetaken at a magnification of 3,000×) of the structure of a sinteredproduct in Example 4 (the cumulative number of ball mill revolutions:3,181,680, sintering temperature: 1,300° C.) (a bar scale in thephotograph: 1 μm).

FIG. 11 is a medium-magnification scanning electron micrograph (an imagetaken at a magnification of 5,000×) of the structure of a sinteredproduct in Example 4 (the cumulative number of ball mill revolutions:3,181,680, sintering temperature: 1,300° C.) (a bar scale in thephotograph: 1 μm).

FIG. 12 is a high-magnification scanning electron micrograph (an imagetaken at a magnification of 10,000×) of the structure of a sinteredproduct in Example 4 (the cumulative number of ball mill revolutions:3,181,680, sintering temperature: 1,300° C.) (a bar scale in thephotograph: 1 μm).

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will next be described in detail.

1. First Embodiment 1-1. Components and Structure of Sputtering Target

An FePt—C-based sputtering target according to a first embodiment of thepresent invention contains Fe, Pt, and C (carbon). The FePt—C-basedsputtering target is characterized in that it has a structure in whichan FePt alloy phase and a C phase containing unavoidable impurities aremutually dispersed, the FePt alloy phase containing Pt in an amount of40 at % or more and 60 at % or less with the balance being Fe andunavoidable impurities, and that the content of C is 21 at % or more and70 at % or less based on the total amount of the target.

1-1-1. FePt Alloy

The FePt alloy can have an fct structure with high magnetocrystallineanisotropy when subjected to heat treatment at high temperature (e.g.,600° C. or higher). Therefore, the FePt alloy has a role in serving as arecording layer of a magnetic recording medium and is a main componentof the FePt—C-based sputtering target according to the embodiments ofthe present invention.

The reason that the content of Pt in the FePt alloy phase is defined tobe 40 at % or more and 60 at % or less is that, when the content of Ptin the FePt alloy phase is outside the range of 40 at % or more and 60at % or less, the fct (ordered face centered tetragonal) structure maynot appear. The content of Pt in the FePt alloy phase is preferably 45at % or more and 55 at % or less, more preferably 49 at % or more and 51at % or less, and particularly preferably 50 at %, from the viewpointthat the fct (ordered face centered tetragonal) structure appearsreliably in the FePt alloy phase.

1-1-2. C (Carbon)

C (carbon) has a role in serving as partitions separating FePt alloyparticles, which are magnetic particles, from each other in an FePtClayer to be obtained by sputtering so as to reduce and uniformize thesize of the FePt alloy particles in the FePtC layer and is one of themain components of the FePt—C-based sputtering target according to thefirst embodiment.

The reason that the content of C is set to be 21 at % or more and 70 at% or less based on the total amount of the target is that C can form thepartitions separating the FePt alloy particles, which are magneticparticles, from each other in the FePtC layer to be obtained bysputtering so that the effect of reducing and uniformizing the size ofthe FePt alloy particles is achieved. If the content of C is less than21 at %, this effect may not be sufficiently achieved. If the content ofC exceeds 70 at %, the number of FePt alloy particles per unit volume ofthe FePtC layer to be obtained by sputtering becomes small in the FePtClayer, and this is disadvantageous for storage capacity. The content ofC is preferably 30 at % or more and 65 at % or less based on the totalamount of the target and more preferably 38 at % or more and 62 at % orless, from the viewpoint of achieving the effect of reducing anduniformizing the size of the FePt particles in the FePtC layer and fromthe viewpoint of the storage capacity of the FePtC layer to be formed.

1-1-3. Structure of Target

In the structure of the FePt—C-based sputtering target according to thefirst embodiment of the present invention, the FePt alloy phasecontaining Pt in an amount of 40 at % or more and 60 at % or less withthe balance being Fe and unavoidable impurities and the C (carbon) phasecontaining unavoidable impurities are mutually dispersed.

The reason that the FePt—C-based sputtering target according to thefirst embodiment has the structure in which the FePt alloy phase and theC phase are mutually dispersed is to prevent certain regions from beingsputtered at an excessive high rate during sputtering to improve thesputtering.

It is preferable to reduce the size of the C phase in the target as muchas possible, in order to reduce the difference in sputtering rate atdifferent positions. Therefore, the average size of the C phase in thetarget is preferably 0.6 μm or less as determined by the interceptmethod, more preferably 0.53 μm or less, and particularly preferably0.45 μm or less.

With the present size reduction technique, it is necessary to increasethe mixing time of the FePt alloy powder and the C powder, in order toreduce the average size of the C phase in the target. Therefore, it isnot realistic to reduce the average size to a large extent with thepresent size reduction technique. When the average size of the C phasein the target is small to a certain extent, the problem with thedifference in sputtering rate at different positions does notparticularly occur. Therefore, a lower limit may be set on the averagesize of the C phase in the target. When the lower limit is set, theaverage size of the C phase in the target, i.e., the average phase sizedetermined by the intercept method, is preferably 0.2 μm or more and 0.6μm or less, more preferably 0.25 μm or more and 0.53 μm or less, andparticularly preferably 0.33 μm or more and 0.45 μm or less, also inconsideration of the cost with the present size reduction technique.

In the present description, the average size of the C phase isdetermined by the intercept method in the following manner.

First, a total of five lines are drawn on an SEM photograph of a crosssection of a target (an image taken at a magnification of 10,000×). Morespecifically, two horizontal lines are drawn on the cross-section of thetarget in a left-right direction such that the image is dividedvertically into thirds, and three vertical lines are drawn in a verticaldirection such that the image is divided horizontally into quarters.

For each of the five lines, the total length of line segmentsintersecting the C phase and the number of the C phase intersected bythe line are determined. Then the average of the lengths of the segmentsof the five lines that intersect the C phase is determined (by dividingthe total length of the line segments intersecting the C phase by thenumber of the C phases intersected by the lines), and the obtained valueis used as the average size of the C phase determined by the interceptmethod.

In order to perform sputtering favorably, it is preferable that therelative density of the target be large because the larger the value ofthe relative density, the smaller the volume of voids in the target.More specifically, the relative density of the target is preferably 90%or higher. To increase the relative density of the target, it ispreferable to mix the FePt alloy powder and the C powder sufficiently toreduce the particle size of the C powder, as described later. The sizeof the C phase in the target is thereby reduced, and the voids in thetarget can be filled by the plastic flow of the FePt alloy duringsintering, so that the relative density increases.

The content of oxygen is preferably 100 mass ppm or less based on thetotal mass of the target, and the content of nitrogen is preferably 30mass ppm or less based on the total mass of the target. When the contentof oxygen and the content of nitrogen in the target are small asdescribed above, the content of oxygen and the content of nitrogen inthe FePtC layer to be obtained by sputtering are also small, so that theFePtC layer obtained is favorable.

1-2. Production Process

The FePt—C-based sputtering target according to the first embodiment canbe produced by: adding C powder containing unavoidable impurities toFePt alloy powder containing Pt in an amount of 40 at % or more and 60at % or less with the balance being Fe and unavoidable impurities;mixing the C powder and the FePt alloy powder in an atmospherecontaining oxygen to produce a powder mixture; and then molding theproduced powder mixture while the powder mixture is heated underpressure.

In this production process, since the FePt alloy powder and the C powderare mixed in the atmosphere containing oxygen to produce the powdermixture, oxygen is adsorbed on newly formed fresh C surfaces to someextent during mixing. Therefore, when a mixing container is open to theair during or after mixing, oxygen is unlikely to be exponentiallyadsorbed on the surfaces of the C particles, so that ignition of the Cpowder is suppressed. Therefore, the FePt—C-based sputtering target canbe produced stably.

In this production process, Fe and Pt are supplied in the form of FePtalloy powder and are not supplied as a single powder of Fe and a singlepowder of Pt. A single powder of Fe has high activity and may ignite inthe air. However, when Fe and Pt are alloyed to form FePt alloy powder,the activity of Fe can be reduced although it is in the form of powder.Thus, with this production process, ignition of Fe during mixing withthe C powder and ignition of Fe when the mixing container is open to theair after completion of mixing can be suppressed.

1-2-1. Production of FePt Alloy Powder

No particular limitation is imposed on the process for producing theFePt alloy powder. However, in this embodiment, an atomizing method isperformed using a molten FePt alloy containing Pt in an amount of 40 at% or more and 60 at % or less with the balance being Fe and unavoidableimpurities to produce FePt alloy powder having the same composition asthat of the molten FePt alloy.

When the FePt alloy powder contains Pt in an amount of 40 at % or moreand 60 at % or less, the FePt alloy phase in the target obtained bysintering of the FePt alloy powder also contains Pt in an amount of 40at % or more and 60 at % or less, so that the fct structure is morelikely to appear in an FePt phase in an FePtC layer obtained bysputtering using the above target.

Preferably, the FePt alloy powder is produced by an atomizing method.This is because of the following reason. In an atomizing method, rawmetals (Fe and Pt) are first heated to high temperature to form moltenmetals. In this stage, alkali metals such as Na and K, alkaline-earthmetals such as Ca, and gaseous impurities such as oxygen and nitrogenare volatilized and removed to the outside, so that the amount ofimpurities in the FePt alloy powder can be reduced. When a gas atomizingmethod is used, the amount of impurities in the FePt alloy powder can befurther reduced by performing atomizing using argon gas or nitrogen gas.

The target obtained using the FePt alloy powder obtained by an atomizingmethod contains a reduced amount of impurities, so that the content ofoxygen in the target can be suppressed to 100 mass ppm or less. Inaddition, the content of nitrogen can be suppressed to 30 mass ppm orless.

Therefore, sputtering performed using the target is favorable, and anFePtC film to be obtained is also favorable.

Examples of an applicable atomizing method include, for example, a gasatomizing method and a centrifugal atomizing method.

1-2-2. Mixing

The powder mixture is produced by mixing C powder having an averageparticle diameter of, for example, 20 nm or more and 100 nm or less withthe FePt alloy powder obtained by an atomizing method described above sothat the content of C is 21 at % or more and 70 at % or less based onthe total amount of the powder mixture.

When the FePt alloy powder and the C powder are mixed, the particlediameter of the C powder decreases as the mixing of the FePt alloypowder and the C powder proceeds, and fresh C surfaces newly appear.However, by performing the mixing in an atmosphere containing oxygen,the oxygen is adsorbed also on the newly appearing fresh C surfaces.Therefore, at least a certain amount of oxygen has already been adsorbedon the surfaces of the C particles at the point of time of completion ofmixing. Even when the mixing container is opened to introduce the air,the amount of oxygen adsorbed on the surfaces of the C particles doesnot increase exponentially, and ignition of the C particles by heat ofadsorption is unlikely to occur. As described in a Comparative Examplelater, when the FePt alloy powder and the C powder are mixed in anatmosphere containing no oxygen, no oxygen is adsorbed on newlyappearing fresh C surfaces. Therefore, when the mixing container is opento the air after completion of mixing, a large amount of oxygen isimmediately adsorbed on the surfaces of the C particles, and heat ofadsorption is exponentially generated. This increases the possibility ofignition of the C particles.

From the viewpoint of allowing a sufficient amount of oxygen to beadsorbed on the surfaces of the C particles at the point of time ofcompletion of mixing, it is preferable that oxygen be continuouslysupplied from the outside of the mixing container to the atmosphere usedduring mixing. By supplying oxygen continuously, a shortage of oxygen inthe atmosphere is unlikely to occur, so that a sufficient amount ofoxygen is easily adsorbed on the surfaces of the C particles duringmixing.

However, if the amount of oxygen in the atmosphere during mixing of theFePt alloy powder and the C powder is too large, the C powder may igniteduring mixing.

From the viewpoint of allowing a sufficient amount of oxygen to beadsorbed on the surfaces of the C particles at the point of time ofcompletion of mixing and from the viewpoint that the C particles mayignite during mixing if the amount of oxygen in the atmosphere is toolarge, the concentration of oxygen in the atmosphere during mixing ispreferably 10 vol % or higher and 30 vol % or lower, more preferably 15vol % or higher and 25 vol % or lower, and particularly preferably 19vol % or higher and 22 vol % or lower.

Oxygen may be supplied to the atmosphere during mixing by supplying air.This can reduce cost.

The atmosphere during mixing may be composed substantially of an inertgas and oxygen. In this case, incorporation of impurities from theatmosphere into the mixture particles can be suppressed. For example,argon, nitrogen, etc. may be used as the inert gas.

The atmosphere during mixing may be released to the air at some point inthe mixing step. Even when the atmosphere is short of oxygen at somepoint in the mixing step, oxygen can be introduced from the air byreleasing the atmosphere into the air, so that the shortage of oxygencan be mitigated.

1-2-3. Molding Method

No particular limitation is imposed on the method for molding the powdermixture produced as described above while the powder mixture is heatedunder pressure. For example, a hot pressing method, a hot isostaticpressing method (HIP method), a spark plasma sintering method (SPSmethod), etc. may be used. Preferably, when implementing the presentinvention, such a molding method is performed in a vacuum or an inertgas atmosphere. In this case, even when the powder mixture contains acertain amount of oxygen, the amount of oxygen in the sintered productobtained is reduced.

1-3. Effects

Patent Literature 2 (Japanese Patent Application Laid-Open No.2006-161082) discloses a process for producing a sputtering targetformed of a PtFe-based alloy by casting. However, it is difficult toincrease the content of C (carbon) by using casting, because of thesolubility limit of C in the alloy, separation due to the difference inspecific gravity between C and the alloy, etc. In claims 2 and 3 andparagraph 0017 in Patent Literature 2 (Japanese Patent ApplicationLaid-Open No. 2006-161082), C is a choice among a plurality of choicesfor the element added to the PtFe-based alloy, but the content of theelement is 20 at % at the maximum.

However, the production process in the first embodiment uses a sinteringmethod, and therefore the content of C based on the total amount of thetarget can be increased. More specifically, an FePt—C-based sputteringtarget containing a large amount, e.g., 21 at % or more and 70 at % orless, of C can be produced. Therefore, when sputtering is performedusing the FePt—C-based sputtering target according to the firstembodiment, the content of carbon in an FePtC thin film obtained can beincreased.

In the production process in the first embodiment, the FePt alloy powderand the C powder are mixed in an atmosphere containing oxygen.Therefore, at least a certain amount of oxygen has already been adsorbedon the surfaces of the C particles at the point of time of completion ofmixing. Thus, even when the mixing container is opened after completionof mixing to introduce the air, oxygen is unlikely to be exponentiallyadsorbed on the C particles, so that ignition of the C particles issuppressed. Accordingly, although the content of C is large, i.e., 21 at% or more and 70 at % or less based on the total amount of the target,the FePt—C-based sputtering target can be stably produced.

In the production process in the first embodiment, Fe and Pt are alloyedto form an FePt alloy powder. In this manner, the activity of Fe can bereduced although it is in the form of powder, and ignition of Fe duringmixing with the C powder can be suppressed.

2. Second Embodiment 2-1. Components and Structure of Sputtering Target

The FePt—C-based sputtering target according to the first embodimentcontains Fe and Pt as the alloy components. However, an FePt—C-basedsputtering target according to a second embodiment of the presentinvention further contains, as an alloy component, a metal element otherthan Fe and Pt, i.e., Cu. This is the difference from the FePt—C-basedsputtering target according to the first embodiment. Namely, theFePt—C-based sputtering target according to the second embodiment of thepresent invention contains Fe, Pt, and C and further contains Cu, whichis a metal element other than Fe and Pt. The FePt—C-based sputteringtarget is characterized in that it has a structure in which anFePt-based alloy phase and a C phase containing unavoidable impuritiesare mutually dispersed, the FePt-based alloy phase containing Pt in anamount of 40 at % or more and less than 60 at % and Cu in an amount ofmore than 0 at % and 20 at % or less with the balance being Fe andunavoidable impurities and with the total amount of Pt and Cu being 60at % or less, and that the content of C is 21 at % or more and 70 at %or less based on the total amount of the target.

2-1-1. FePtCu Alloy

In the FePt—C-based sputtering target according to the second embodimentof the present invention, Cu is added to an FePt alloy to form an FePtCualloy. When Cu is contained, the temperature of the heat treatment forconverting the crystal structure of the FePt-based alloy to the fctstructure can be reduced (to, for example, 600° C.), so that the cost ofthe heat treatment on an FePtC layer obtained by sputtering can bereduced. In addition, the addition of Cu may allow the crystal structureof the obtained FePtC layer to be converted to the fct structure by heatgenerated during sputtering without additional heat treatment.

The reason that the content of Pt in the FePtCu alloy phase in thesecond embodiment is defined to be 40 at % or more and less than 60 at %is that, when the content of Pt in the FePtCu alloy phase is outside therange of 40 at % or more and less than 60 at %, the fct (ordered facecentered tetragonal) structure may not appear. The content of Pt in theFePtCu alloy phase is preferably 45 at % or more and 55 at % or less andmore preferably 49 at % or more and 51 at % or less, from the viewpointthat the fct (ordered face centered tetragonal) structure appearsreliably in the FePtCu alloy phase. However, it is premised that thetotal content of Fe and Pt is less than 100 at %, that the content of Cuis more than 0 at % and 20 at % or less, and that the total content ofPt and Cu is 60 at % or less.

A metal other than Cu can be added to the FePt alloy, and examplesthereof include Ag, Mn, Ni, Co, Pd, Cr, V, and B.

2-1-2. C (Carbon)

The role of C (carbon) is the same as that described above in the firstembodiment. More specifically, C (carbon) has a role in serving aspartitions separating FePtCu alloy particles, which are magneticparticles, from each other in an FePtCuC layer to be obtained bysputtering to reduce and uniformize the size of the FePtCu particles inthe FePtCuC layer and is one of the main components of the FePt—C-basedsputtering target according to the second embodiment.

The reason that the content of C is set to be 21 at % or more and 70 at% or less based on the total amount of the target is the same as thatdescribed above in the first embodiment. More specifically, the reasonis that C can form the partitions separating the FePtCu alloy particles,which are magnetic particles, from each other in the FePtCuC layer to beobtained by sputtering so that the effect of reducing and uniformizingthe size of the FePtCu alloy particles is achieved. If the content of Cis less than 21 at %, this effect may not be sufficiently achieved. Ifthe content of C exceeds 70 at %, the number of FePtCu alloy particlesper unit volume of the FePtCuC layer to be obtained by sputteringbecomes small in the FePtCuC layer, and this is disadvantageous forstorage capacity. The content of C is preferably 30 at % or more and 65at % or less based on the total amount of the target and more preferably38 at % or more and 62 at % or less, from the viewpoint of achieving theeffect of reducing and uniformizing the size of the FePtCu particles inthe FePtCuC layer and from the viewpoint of the storage capacity of theFePtCuC layer to be formed.

2-1-3. Structure of Target

In the structure of the FePt—C-based sputtering target according to thesecond embodiment of the present invention, the FePt-based alloy phaseand the C phase containing unavoidable impurities are mutuallydispersed. The FePt-based alloy phase contains Pt in an amount of 40 at% or more and less than 60 at % and Cu in an amount of more than 0 at %and 20 at % or less with the balance being Fe and unavoidable impuritiesand with the total amount of Pt and Cu being 60 at % or less. Thecontent of C is 21 at % or more 70 at % or less based on the totalamount of the target.

The reason that the FePt—C-based sputtering target according to thesecond embodiment has the structure in which the FePtCu alloy phase andthe C phase are mutually dispersed is the same as that described abovein the first embodiment. More specifically, the reason is to preventcertain regions from being sputtered at an excessive high rate duringsputtering to improve the sputtering.

The size of the C phase in the target, i.e., the average size of thephase determined by the intercept method, is preferably 0.6 μm or less,more preferably 0.53 μm or less, and particularly preferably 0.45 μm orless, for the same reason as that for the FePt—C-based sputtering targetaccording to the first embodiment. As in the FePt—C-based sputteringtarget according to the first embodiment, a lower limit may be set onthe size of the C phase in the target. When the lower limit is set, theaverage size of the C phase in the target, i.e., the average phase sizedetermined by the intercept method, is preferably 0.2 μm or more and 0.6μm or less, more preferably 0.25 μm or more and 0.53 μm or less, andparticularly preferably 0.33 μm or more and 0.45 μm or less, also inconsideration of the cost with the present size reduction technique.

As in the FePt—C-based sputtering target according to the firstembodiment, in order to perform sputtering favorably, it is preferablethat the relative density of the target be large because the larger thevalue of the relative density, the smaller the volume of voids in thetarget. More specifically, the relative density of the target ispreferably 90% or higher. To increase the relative density of thetarget, it is preferable to mix the FePtCu alloy powder and the C powdersufficiently to reduce the particle size of the C powder, as describedlater. The size of the C phase in the target is thereby reduced, and thevoids in the target can be filled by the plastic flow of the FePtCualloy during sintering, so that the relative density increases.

As in the FePt—C-based sputtering target according to the firstembodiment, the content of oxygen is preferably 100 mass ppm or lessbased on the total mass of the target, and the content of nitrogen ispreferably 30 mass ppm or less based on the total mass of the target.When the content of oxygen and the content of nitrogen in the target aresmall as described above, the content of oxygen and the content ofnitrogen in the FePtCuC layer to be obtained by sputtering are alsosmall, so that the FePtCuC layer obtained is favorable.

2-2. Production Process

The FePt—C-based sputtering target according to the second embodimentcan be produced by: adding C powder containing unavoidable impurities toFePtCu alloy powder containing Pt in an amount of 40 at % or more andless than 60 at % and Cu in an amount of more than 0 at % and 20 at % orless with the balance being Fe and unavoidable impurities and with thetotal amount of Pt and Cu being 60 at % or less; mixing the C powder andthe FePtCu alloy powder in an atmosphere containing oxygen to produce apowder mixture; and molding the produced powder mixture while themixture is heated under pressure.

In this production process, since the FePtCu alloy powder and the Cpowder are mixed in the atmosphere containing oxygen to produce thepowder mixture, oxygen is adsorbed on newly formed fresh C surfaces tosome extent during mixing. Therefore, when a mixing container is open tothe air during or after mixing, oxygen is unlikely to be exponentiallyadsorbed on the surfaces of the C particles, so that ignition of the Cpowder is suppressed. Therefore, the FePt—C-based sputtering target canbe produced stably.

In this production process, as in the process for producing the targetin the first embodiment, Fe is not supplied as a single powder. Fe, Pt,and Cu are supplied as the FePtCu alloy powder and are not supplied as asingle powder of Fe, a single powder of Pt, and a single powder of Cu. Asingle powder of Fe has high activity and may be ignite in the air.However, when Fe, Pt, and Cu are alloyed to form an FePtCu alloy powder,the activity of Fe can be reduced although it is in the form of powder.Therefore, with this production process, as with the process forproducing the target in the first embodiment, ignition of Fe duringmixing with the C powder and ignition of Fe when the mixing container isopen to the air after completion of mixing can be suppressed.

2-2-1. Production of FePtCu Alloy Powder

No particular limitation is imposed on the process for producing theFePtCu alloy powder. However, in this production process, an atomizingmethod is performed using a molten FePtCu alloy containing Pt in anamount of 40 at % or more and less than 60 at % and Cu in an amount ofmore than 0 at % and 20 at % or less with the balance being Fe andunavoidable impurities and with the total amount of Pt and the one ormore kinds of metal elements being 60 at % or less to produce FePtCualloy powder having the same composition as that of the molten FePtCualloy.

When the FePtCu alloy powder contains Pt in an amount of 40 at % or moreand less than 60 at % and Cu in an amount of more than 0 at % and 20 at% or less (provided that the total amount of Pt and Cu is 60 at % orless), the FePtCu alloy phase in the target obtained by sintering theFePtCu alloy powder also contains Pt in an amount of 40 at % or more andless than 60 at % and Fe in an amount of 40 at % or more and less than60 at %. Therefore, the fct structure is more likely to appear in anFePtCu phase in the FePtCuC layer obtained by sputtering using thetarget.

As in the process for producing the target in the first embodiment, theFePtCu alloy powder is preferably produced by an atomizing method. Thisis because of the following reason. In an atomizing method, raw metals(Fe, Pt, and Cu) are first heated to high temperature to form moltenmetals. In this stage, alkali metals such as Na and K, alkaline-earthmetals such as Ca, and gaseous impurities such as oxygen and nitrogenare volatilized and removed to the outside, so that the amount ofimpurities in the FePtCu alloy powder can be reduced. When a gasatomizing method is used, the amount of impurities in the FePtCu alloypowder can be further reduced by performing atomizing using argon gas ornitrogen gas.

The target obtained using the FePtCu alloy powder obtained by anatomizing method contains a reduced amount of impurities, so that thecontent of oxygen in the target can be suppressed to 100 mass ppm orless. In addition, the content of nitrogen can be suppressed to 30 massppm or less.

Therefore, sputtering performed using the target is favorable, and anFePtCuC film to be obtained is also favorable.

Examples of an applicable atomizing method include, for example, a gasatomizing method and a centrifugal atomizing method.

2-2-2. Mixing

In this production process, as in the process for producing the targetin the first embodiment, the powder mixture is produced by mixing Cpowder having an average particle diameter of, for example, 20 nm ormore and 100 nm or less with the FePt alloy powder obtained by anatomizing method described above such that the content of C is 21 at %or more and 70 at % or less based on the total amount of the powdermixture.

When the FePtCu alloy powder and the C powder are mixed, the particlediameter of the C powder decreases as the mixing of the FePtCu alloypowder and the C powder proceeds, and fresh C surfaces newly appear.However, by performing the mixing in an atmosphere containing oxygen, aswith the process for producing the target in the first embodiment, theoxygen is adsorbed also on the newly appearing fresh C surfaces.Therefore, at least a certain amount of oxygen has already been adsorbedon the surfaces of the C particles at the point of time of completion ofmixing. Even when the mixing container is opened to introduce the air,the amount of oxygen adsorbed on the surfaces of the C particles doesnot increase exponentially, and ignition of the C particles by heat ofadsorption is unlikely to occur.

From the viewpoint of allowing a sufficient amount of oxygen to beadsorbed on the surfaces of the C particles at the point of time ofcompletion of mixing, in this production process, as in the process forproducing the target in the first embodiment, it is preferable thatoxygen be continuously supplied from the outside of the mixing containerto the atmosphere used during mixing. By supplying oxygen continuously,a shortage of oxygen in the atmosphere is unlikely to occur, so that asufficient amount of oxygen is easily adsorbed on the surfaces of the Cparticles during mixing.

However, if the amount of oxygen in the atmosphere during mixing of theFePtCu alloy powder and the C powder is too large, the C powder mayignite during mixing.

From the viewpoint of allowing a sufficient amount of oxygen to beadsorbed on the surfaces of the C particles at the point of time ofcompletion of mixing and from the viewpoint that the C particles mayignite during mixing if the amount of oxygen in the atmosphere is toolarge, in this production process, as in the process for producing thetarget in the first embodiment, the concentration of oxygen in theatmosphere during mixing is preferably 10 vol % or higher and 30 vol %or lower, more preferably 15 vol % or higher and 25 vol % or lower, andparticularly preferably 19 vol % or higher and 22 vol % or lower.

Oxygen may be supplied to the atmosphere during mixing by supplying air.This can reduce cost.

The atmosphere during mixing may be composed substantially of an inertgas and oxygen. In this case, incorporation of impurities from theatmosphere into the mixture particles can be suppressed. For example,argon, nitrogen, etc. may be used as the inert gas.

The atmosphere during mixing may be released to the air at some point inthe mixing step. Even when the atmosphere is short of oxygen at somepoint in the mixing step, oxygen can be introduced from the air byreleasing the atmosphere into the air, so that the shortage of oxygencan be mitigated.

2-2-3. Molding Method

In this production process, no particular limitation is imposed on themethod for molding the powder mixture produced as described above whilethe powder mixture is heated under pressure. In this production process,as in the process for producing the target in the first embodiment, forexample, a hot pressing method, a hot isostatic pressing method (HIPmethod), a spark plasma sintering method (SPS method), etc. may be used.Preferably, when implementing the present invention, such a moldingmethod is performed in a vacuum or an inert gas atmosphere. In thiscase, even when the powder mixture contains a certain amount of oxygen,the amount of oxygen in the sintered product obtained is reduced.

The production process in the second embodiment, as the productionprocess in the first embodiment, uses a sintering method, and thereforethe content of C based on the total amount of the target can beincreased. More specifically, an FePt—C-based sputtering targetcontaining a large amount, e.g., 21 at % or more and 70 at % or less, ofC can be produced. Therefore, when sputtering is performed using theFePt—C-based sputtering target according to the second embodiment, thecontent of carbon in an FePtC thin film obtained can be increased.

In the production process in the second embodiment, the FePtCu alloypowder and the C powder are mixed in an atmosphere containing oxygen.Therefore, at least a certain amount of oxygen has already been adsorbedon the surfaces of the C particles at the point of time of completion ofmixing. Thus, even when the mixing container is opened after completionof mixing to introduce the air, oxygen is unlikely to be exponentiallyadsorbed on the C particles, so that ignition of the C particles issuppressed. Accordingly, although the content of C is large, i.e., 21 at% or more and 70 at % or less based on the total amount of the target,the FePt—C-based sputtering target can be stably produced.

In the production process in the second embodiment, Fe, Pt, and Cu arealloyed to form an FePtCu alloy powder. In this manner, the activity ofFe can be reduced although it is in the form of powder, and ignition ofFe during mixing with the C powder can be suppressed.

EXAMPLES Example 1

The target compositions of a powder mixture and a target in Example 1are 40(50Fe-50Pt)-60C. More specifically, the target composition of themetal components is 50 at % Fe-50 at % Pt, and the target compositionalratios of the FePt alloy and C (carbon) are 40 at % for the FePt alloyand 60 at % for C. However, as described later, since part of C (carbon)is volatilized during production of the powder mixture and duringsintering of the target, the compositional ratios of the FePt alloy andC (carbon) in the powder mixture and target obtained slightly deviatefrom the target values. When the content of C (carbon) is representednot by at % but by vol %, the target compositions of the powder mixtureand target in Example 1 are (50Fe-50Pt)-49.6 vol % C.

The metals in bulk form were weighed such that the composition of thealloy was Fe: 50 at % and Pt: 50 at % and then heated by high frequencyheating to form a molten Fe—Pt alloy at 1,800° C. Then a gas atomizingmethod using argon gas was performed to produce 50 at % Fe-50 at % Ptalloy powder. The average particle diameter of the obtained alloy powderwas measured using Microtrac MT3000 manufactured by NIKKISO Co., Ltd.and found to be 50 μm.

89.03 g of C powder having an average particle diameter of 35 μm and abulk density of 0.25 g/cm³ was added to 620.00 g of the obtained Fe—Ptalloy powder such that the content of C was 60 at % based on the totalamount of the powder, and then these components were mixed using a ballmill until the cumulative number of revolutions reached 4,136,400 tothereby produce a powder mixture. Hereinafter, the cumulative number ofrevolutions of the ball mill may be referred to as the cumulative numberof ball mill revolutions or simply as the number of revolutions.

A mixing container was covered with a lid during mixing. However, anintroduction port for introducing outside air and a discharge port fordischarging were provided in the mixing container, and fresh air wasalways circulated in the mixing container, so that the amount of oxygenin the mixing container was always the same as that in the air.

When the cumulative number of ball mill revolutions reached 935,280,2,535,840, and 4,136,400, the lid of the mixing container was opened,and the powder mixture was taken out. Then the contents of oxygen andnitrogen in the powder mixture were measured using a TC-600 SeriesNitrogen/Oxygen Determinator manufactured by LECO Corporation, and thecontent of carbon was measured using a Carbon/Sulfur Analyzermanufactured by HORIBA, Ltd. In addition, whether or not ignition hadoccurred was visually checked when the lid of the mixing container wasopened. These results are shown in TABLE 1 below.

TABLE 1 Cumulative number of ball mill Nitrogen revolutions Oxygen (massCarbon (Number) (mass %) ppm) (mass %) Ignition 0 0.2 130 12.55 No935,280 1.37 1,300 12.33 No 2,535,840 1.85 1,293 12.12 No 4,136,400 2.301,293 11.78 No

When the cumulative number of ball mill revolutions reached 935,280,2,535,840, and 4,136,400, the mixing container was opened, and whetheror not ignition had occurred was visually checked. However, no ignitionwas found at each point.

As the cumulative number of ball mill revolutions increases, the contentof oxygen in the powder mixture increases, but the content of carbondecreases. This may be because, as the mixing proceeds, the adsorptionof oxygen to the C powder proceeds, but part of carbon reacts withoxygen and volatilizes as CO and CO₂. The content of nitrogen in thepowder mixture was substantially constant after the cumulative number ofball mill revolutions reached 935,280.

The powder mixture mixed until the cumulative number of ball millrevolutions reached 4,136,400 was subjected to hot pressing under theconditions of temperature: 1,460° C., pressure: 25 MPa, time: 45 min.,atmosphere: a vacuum of 5×10⁻² Pa or lower to thereby produce a sinteredproduct.

The density of the produced sintered product was measured by theArchimedes method, and the measured value was divided by a theoreticaldensity to determine the relative density. The results are shown inTABLE 2 below. The content of carbon in the sintered product actuallymeasured (see TABLE 3) was used as the amount of carbon used to computethe theoretical density, that is to say, the theoretical density wascomputed in consideration of a reduction in the amount of carbon duringmixing and sintering.

TABLE 2 Measured density Theoretical Relative density (g/cm³) density(g/m³) (%) 8.91 9.24 96.4

The relative density was high, i.e., 96.4%, so that the amount of voidsin the obtained sintered product was small.

The contents of oxygen and nitrogen in the sintered product weremeasured using a TC-600 Series Nitrogen/Oxygen Determinator manufacturedby LECO Corporation, and the content of carbon was measured using aCarbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The measurementresults are shown in TABLE 3 below. In the below TABLE 3, themeasurement results for the non-sintered powder mixture (the cumulativenumber of ball mill revolutions: 4,136,400) are also shown forcomparison.

TABLE 3 Oxygen Nitrogen Carbon (mass %) (mass ppm) (mass %) Powdermixture before 2.30 1293 11.78 sintering Sintered product 0.0045 2 11.56(Sintering temperature: 1,460° C.)

The content of oxygen in the powder mixture mixed until the cumulativenumber of ball mill revolutions reached 4,136,400 was 2.30 mass %.However, the content of oxygen in the sintered product obtained by hotpressing of the powder mixture in a vacuum was 0.0045 mass % (45 massppm), i.e., was reduced to about 1/511, and a significant reduction wasfound. Therefore, it was found that, even when mixing was performed inan atmosphere containing oxygen and a large amount of oxygen wasadsorbed on the C powder during mixing, the adsorbed oxygen wasvolatilized during sintering, and almost no oxygen was introduced intothe sintered product.

The content of nitrogen in the sintered product obtained by hot pressingwas reduced to about 1/647, and a significant reduction was found.

The content of carbon was slightly reduced by hot pressing. This may bebecause carbon reacts with oxygen adsorbed on the surface during hotpressing and volatilizes as CO and CO₂.

The structure of the obtained sintered product (the cumulative number ofball mill revolutions: 4,136,400, sintering temperature: 1,460° C.) wasobserved under a scanning electron microscope (SEM). FIGS. 1, 2, and 3show SEM photographs of the sintered product. FIG. 1 is an SEMphotograph at a low magnification (an image taken at a magnification of3,000×) (a bar scale in the photograph represents 1 μm). FIG. 2 is anSEM photograph at a medium magnification (an image taken at amagnification of 5,000×) (a bar scale in the photograph represents 1μm), and FIG. 3 is an SEM photograph at a high magnification (an imagetaken at a magnification of 10,000×) (a bar scale in the photographrepresents 1 μm). In FIGS. 1, 2, and 3, dark gray regions are the Cphase, and white regions are the FePt alloy phase. As can be seen fromFIGS. 1, 2, and 3, fine regions of the C phase are dispersed in theentire area of the structure.

Next, the size of the phase in the obtained sintered product (thecumulative number of ball mill revolutions: 4,136,400, sinteringtemperature: 1,460° C.) was determined by the intercept method.

Specifically, a total of five lines were drawn on the SEM photograph ofthe cross section of the target in FIG. 3 (an image taken at amagnification of 10,000×). More specifically, two horizontal lines weredrawn on the SEM photograph of FIG. 3 in a left-right direction suchthat the image was divided vertically into thirds, and three verticallines were drawn in a vertical direction such that the image was dividedhorizontally into quarters.

For each of the five lines, the total length of line segmentsintersecting the C phase and the number of the C phase intersected bythe line were determined. Then the average of the lengths of thesegments of the five lines that intersected the C phase was determined(by dividing the total length of the line segments intersecting the Cphase by the number of the C phases intersected by the lines), and theobtained value was used as the average size of the C phase determined bythe intercept method. The results showed that the average size of the Cphase determined by the intercept method was 0.52 μm.

Example 2

A powder mixture and a sintered product were produced in the same manneras in Example 1 except that the mixing container was filled with air andsealed and the FePt powder and C powder were mixed in the sealed mixingcontainer, that the cumulative number of ball mill revolutions waschanged, that the number of times and the timing of introduction offresh air by opening the mixing container during mixing were changed,and that the sintering temperature during production of the sinteredproduct was changed to 1,380° C. and 1,340° C. The target compositionsof the powder mixture and target in Example 2 are the same as those inExample 1 and each are 40(50Fe-50Pt)-60C.

When the cumulative number of ball mill revolutions reached 2,805,840,and 4,073,760, the lid of the mixing container was opened, and thepowder mixture was taken out. Then the contents of oxygen and nitrogenin the powder mixture were measured using a TC-600 SeriesNitrogen/Oxygen Determinator manufactured by LECO Corporation, and thecontent of carbon was measured using a Carbon/Sulfur Analyzermanufactured by HORIBA, Ltd. In addition, whether or not ignition hadoccurred was visually checked when the lid of the mixing container wasopened. These results are shown in TABLE 4 below.

TABLE 4 Cumulative number of ball mill Nitrogen revolutions Oxygen (massCarbon (Number) (mass %) ppm) (mass %) Ignition 0 0.2 130 12.55 No2,805,840 2.28 3,200 12.31 No 4,073,760 1.98 2,870 12.08 No

When the cumulative number of ball mill revolutions reached 935,280,1,870,560, 2,805,840, and 4,073,760, the mixing container was opened,and whether or not ignition had occurred was visually checked. However,no ignition was found at each point.

At the point of time when the cumulative number of ball mill revolutionswas 2,805,840, the content of oxygen in the powder mixture increased 114times as compared to that before mixing was started (the number ofrevolutions: 0), but the content of carbon decreased. This may bebecause, as the mixing proceeds, the adsorption of oxygen to the Cpowder proceeds, but part of carbon reacts with oxygen and volatilizesas CO and CO₂. At the point of time when the cumulative number of ballmill revolutions was 2,805,840, the content of nitrogen in the powdermixture also increased about 25 times as compared to that before mixingwas started (the number of revolutions: 0).

Next, the powder mixture mixed until the cumulative number of ball millrevolutions reached 2,805,840 was subjected to hot pressing under theconditions of temperature: 1,380° C., pressure: 25 MPa, time: 45 min.,atmosphere: a vacuum of 5×10⁻² Pa or lower to thereby produce a sinteredproduct. In addition, the powder mixture mixed until the cumulativenumber of ball mill revolutions reached 4,073,760 was subjected to hotpressing under the conditions of temperature: 1,340° C., pressure: 25MPa, time: 45 min., atmosphere: a vacuum of 5×10⁻² Pa or lower tothereby produce a sintered product.

The density of each of the produced sintered products was measured bythe Archimedes method, and the measured value was divided by atheoretical density to determine the relative density. The results areshown in TABLE 5 below. The content of carbon in each sintered productshown in TABLE 6 was used as the amount of carbon used to compute thetheoretical density, that is to say, the theoretical density wascomputed in consideration of a reduction in the amount of carbon duringmixing and sintering.

TABLE 5 Sintering Theoretical Relative Sintered powder temperatureDensity density density mixture (° C.) (g/cm³) (g/cm³) (%) Powdermixture 1,380 8.49 9.09 93.4 when number of revolution was 2,805,840Powder mixture 1,340 8.41 9.14 92.0 when number of revolution was4,073,760

The relative densities of the two sintered products were high, i.e.,93.4% and 92.0%, so that the amount of voids in each of the obtainedsintered products was small.

The contents of oxygen and nitrogen in the sintered product weremeasured using a TC-600 Series Nitrogen/Oxygen Determinator manufacturedby LECO Corporation, and the content of carbon was measured using aCarbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The measurementresults are shown in TABLE 3 below. In the below TABLE 6, themeasurement results for the non-sintered powder mixture (the cumulativenumber of ball mill revolutions: 2,805,840, 4,073,760) are also shownfor comparison.

TABLE 6 Oxygen Nitrogen Carbon (mass %) (mass ppm) (mass %) Powdermixture (Cumulative 2.28 3,200 12.31 number of ball mill revolutions:2,805,840) Sintered product (Sintering 0.0048 17 12.04 temperature:1,380° C.) Powder mixture (Cumulative 1.98 2,870 12.08 number of ballmill revolutions: 4,073,760) Sintered product (Sintering 0.0053 21 11.89temperature: 1,340° C.)

The content of oxygen in the powder mixture mixed until the cumulativenumber of ball mill revolutions reached 2,805,840 was 2.28 mass %.However, the content of oxygen in the sintered product obtained by hotpressing of the above powder mixture in a vacuum was 0.0048 mass % (48mass ppm), i.e., was reduced to about 1/475. The content of oxygen inthe powder mixture mixed until the total number of revolutions reached4,073,760 was 1.98 mass %. However, the content of oxygen in thesintered product obtained by hot pressing of the above powder mixture ina vacuum was 0.0053 mass % (53 mass ppm), i.e., was reduced to about1/374. Therefore, it was found that, even when mixing was performed inan atmosphere containing oxygen and a large amount of oxygen wasadsorbed on the C powder during mixing, the adsorbed oxygen wasvolatilized during sintering, and only a little oxygen remained in thesintered product.

The contents of nitrogen in the sintered products were significantlysmaller than those in the powder mixtures.

The contents of carbon were slightly reduced by sintering. This may bebecause carbon reacts with oxygen adsorbed on the surface during hotpressing and volatilizes as CO and CO₂.

The structure of the obtained sintered product (the cumulative number ofball mill revolutions: 4,073,760, sintering temperature: 1,340° C.) wasobserved under a scanning electron microscope (SEM). FIGS. 4, 5, and 6show SEM photographs of the sintered product. FIG. 4 is an SEMphotograph at a low magnification (an image taken at a magnification of3,000×) (a bar scale in the photograph represents 1 μm). FIG. 5 is anSEM photograph at a medium magnification (an image taken at amagnification of 5,000×) (a bar scale in the photograph represents 1μm), and FIG. 6 is an SEM photograph at a high magnification (an imagetaken at a magnification of 10,000×) (a bar scale in the photographrepresents 1 μm). In FIGS. 4, 5, and 6, black regions are the C phase,and white regions are the FePt alloy phase. As can be seen from FIGS. 4,5, and 6, fine regions of the C phase are dispersed in the entire areaof the structure.

Next, the size of the phase in the obtained sintered product (thecumulative number of ball mill revolutions: 4,073,760, sinteringtemperature: 1,340° C.) was determined by the intercept method.

Specifically, a total of five lines were drawn on the SEM photograph ofthe cross section of the target in FIG. 6 (an image taken at amagnification of 10,000×). More specifically, two horizontal lines weredrawn on the SEM photograph of FIG. 6 in a left-right direction suchthat the image was divided vertically into thirds, and three verticallines were drawn in a vertical direction such that the image was dividedhorizontally into quarters.

For each of the five lines, the total length of line segmentsintersecting the C phase and the number of the C phase intersected bythe line were determined. Then the average of the lengths of thesegments of the five lines that intersected the C phase was determined(by dividing the total length of the line segments intersecting the Cphase by the number of the C phases intersected by the lines), and theobtained value was used as the average size of the C phase determined bythe intercept method. The results showed that the average size of the Cphase determined by the intercept method was 0.50 μm.

Example 3

The target compositions of a powder mixture and a target in Example 3are 60(50Fe-50Pt)-40C. More specifically, the target composition of themetal components is 50 at % Fe-50 at % Pt, and the target compositionalratios of the FePt alloy and C (carbon) are 60 at % for the FePt alloyand 40 at % for C. In Examples 1 and 2, the target compositional ratioof C with respect to the total amount is 60 at %. Whereas, in Example 3,the target compositional ratio of C is 40 at %, and the content of C issmaller than that in Examples 1 and 2. However, as described later,since part of C (carbon) is volatilized during production of the powdermixture and during sintering of the target, the compositional ratios ofthe FePt alloy and C (carbon) in the powder mixture and target obtainedslightly deviate from the target values. When the content of C (carbon)is represented not by at % but by vol %, the target compositions of thepowder mixture and target in Example 3 are (50Fe-50Pt)-30.4 vol % C.

Example 3 is different from Example 2 in that the mixing container wasfilled with a gas mixture (Ar-20% O₂) and was sealed and the FePt powderand the C powder were mixed in the sealed mixing container, that thecumulative number of ball mill revolutions was changed, that the numberof times and the timing of introduction of fresh air by opening themixing container during mixing were changed, and that the sinteringtemperature during production of the sintered product was changed to1,250° C. and 1,300° C.

A powder mixture and a sintered product were produced in the same manneras in Example 2 except for the above differences.

When the cumulative number of ball mill revolutions reached 290,520,905,040, 1,195,560, 1,810,080, 2,246,400, and 3,181,680, the mixingcontainer was opened, and whether or not ignition had occurred wasvisually checked. However, no ignition was found at each point.

The powder mixture mixed until the cumulative number of ball millrevolutions reached 1,810,080 was subjected to hot pressing under theconditions of temperature: 1,300° C., pressure: 25 MPa, time: 45 min.,atmosphere: a vacuum of 5×10⁻² Pa or lower to thereby produce a sinteredproduct. In addition, the powder mixture mixed until the cumulativenumber of ball mill revolutions reached 3,181,680 was subjected to hotpressing under the conditions of temperature: 1,250° C., 1,300° C.,pressure: 25 MPa, time: 45 min., atmosphere: a vacuum of 5×10⁻² Pa orlower to thereby produce a sintered product.

The density of each of the produced sintered products was measured bythe Archimedes method, and the measured value was divided by atheoretical density to determine the relative density. The results areshown in TABLE 7 below. The content of carbon in each sintered productshown in TABLE 8 was used as the amount of carbon used to compute thetheoretical density, that is to say, the theoretical density wascomputed in consideration of a reduction in the amount of carbon duringmixing and sintering.

TABLE 7 Sintering Theoretical Relative Sintered powder temperatureDensity density density mixture (° C.) (g/cm³) (g/cm³) (%) Powdermixture 1,300 11.83 11.83 100.0 when cumulative number of ball millrevolutions was 1,810,080 Powder mixture 1,250 11.44 11.80 96.9 whencumulative number of ball mill revolutions was 3,181,680 Powder mixture1,300 11.42 12.00 95.2 when cumulative number of ball mill revolutionswas 3,181,680

The relative densities of the three sintered products were high, i.e.,100.0%, 96.9% and 95.2%, so that the amount of voids in each of theobtained sintered products was small.

The contents of oxygen and nitrogen in each of the sintered productsmolded by sintering of the powder mixtures shown in TABLE 7 at asintering temperature of 1,250° C. or 1,300° C. were measured using aTC-600 Series Nitrogen/Oxygen Determinator manufactured by LECOCorporation, and the content of carbon was measured using aCarbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The measurementresults are shown in TABLE 8 below.

TABLE 8 Oxygen Nitrogen Carbon (mass %) (mass ppm) (mass %) Sinteredproduct 17 0 5.29 (Cumulative number of ball mill revolutions: 181,080,Sintering temperature: 1,300° C.) Sintered product — — 5.38 (Cumulativenumber of ball mill revolutions: 3,181,680, Sintering temperature:1,250° C.) Sintered product 9 1 4.97 (Cumulative number of ball millrevolutions: 3,181,680, Sintering temperature: 1,300° C.)

As shown in TABLE 8, the contents of oxygen and nitrogen in the sinteredproducts were very small.

The structure of the obtained sintered product was observed under ascanning electron microscope (SEM). FIGS. 7, 8, and 9 show SEMphotographs of the sintered product. FIG. 7 is an SEM photograph at alow magnification (an image taken at a magnification of 3,000×) (a barscale in the photograph represents 1 μm). FIG. 8 is an SEM photograph ata medium magnification (an image taken at a magnification of 5,000×) (abar scale in the photograph represents 1 μm), and FIG. 9 is an SEMphotograph at a high magnification (an image taken at a magnification of10,000×) (a bar scale in the photograph represents 1 μm). In FIGS. 7, 8,and 9, black regions are the C phase, and white regions are the FePtalloy phase. As can be seen from FIGS. 7, 8, and 9, fine regions of theC phase are dispersed in the entire area of the structure.

Next, the size of the phase in the obtained sintered product (thecumulative number of ball mill revolutions: 3,181,680, sinteringtemperature: 1,300° C.) was determined by the intercept method.

Specifically, a total of five lines were drawn on the SEM photograph ofthe cross section of the target in FIG. 9 (an image taken at amagnification of 10,000×). More specifically, two horizontal lines weredrawn on the SEM photograph of FIG. 9 in a left-right direction suchthat the image was divided vertically into thirds, and three verticallines were drawn in a vertical direction such that the image was dividedhorizontally into quarters.

For each of the five lines, the total length of line segmentsintersecting the C phase and the number of the C phase intersected bythe line were determined. Then the average of the lengths of thesegments of the five lines that intersected the C phase was determined(by dividing the total length of the line segments intersecting the Cphase by the number of the C phases intersected by the lines), and theobtained value was used as the average size of the C phase determined bythe intercept method. The results showed that the average size of the Cphase determined by the intercept method was 0.33 μm.

Comparative Example 1

A powder mixture and a sintered product were produced in the same manneras in Example 3 except that the mixing container was filled with argon(Ar) and sealed and the FePt powder and the C powder were mixed in thesealed mixing container, that the cumulative number of ball millrevolutions was changed, that the number of times and the timing ofintroduction of fresh air by opening the mixing container during mixingwere changed, and that the sintering temperature during production ofthe sintered product was changed to 1,100° C. In Comparative Example 1,the target compositions of the powder mixture and the target are thesame as those in Example 3 and are 60(50Fe-50Pt)-40C. In Examples 1 and2, the target compositional ratio of C with respect to the total amountis 60 at %. Whereas, in Comparative Example 1, the target compositionalratio of C is 40 at %, and the content of C is smaller than that inExamples 1 and 2.

When the cumulative number of ball mill revolutions reached 209,520,608,040, 1,006,560, 1,405,080, 1,803,600, 2,202,120, and 2,816,640, themixing container was opened, and whether or not ignition had occurredwas visually checked. Until the point of time when the cumulative numberof ball mill revolutions was 2,202,120, no ignition was found. However,at the point of time when the cumulative number of ball mill revolutionswas 2,816,640, ignition was found.

To be precise, the atmosphere in the mixing container during mixing wasthe sealed gas mixture (Ar-20% O₂) atmosphere only in the initial stageof mixing (until the cumulative number of ball mill revolutions reached209,520) and was a sealed argon (Ar) atmosphere thereafter. The mixingwas performed in the sealed gas mixture (Ar-20% O₂) atmosphere only inthe initial stage of mixing (until the cumulative number of ball millrevolutions reached 209,520). This cumulative number of ball millrevolutions is only 7.4% of the final cumulative number of ball millrevolutions, i.e., 2,816,640, so that the amount of oxygen adsorbed onthe surface of the C powder in the initial stage of mixing (until thecumulative number of ball mill revolutions reached 209,520) isconsidered to be small. Therefore, Comparative Example 1 is thought tobe an experimental example in which the FePt powder and the C particleshaving a certain amount or less of oxygen adsorbed thereon are mixed2,816,640−209,520=2,607,120 times in the argon (Ar) atmosphere.

The powder mixture mixed until the cumulative number of ball millrevolutions reached 1,405,080 was subjected to hot pressing under theconditions of temperature: 1,100° C., pressure: 25 MPa, time: 45 min.,atmosphere: a vacuum of 5×10⁻² Pa or lower to thereby produce a sinteredproduct.

The density of each of the produced sintered products was measured bythe Archimedes method, and the measured value was divided by atheoretical density to determine the relative density. The results areshown in TABLE 9 below. In Comparative Example 1, the theoreticaldensity was not computed in consideration of a reduction in the amountof carbon during sintering, as was in Examples 1 to 3.

TABLE 9 Sintering Theoretical Relative Sintered powder temperatureDensity density density mixture (° C.) (g/cm³) (g/cm³) (%) Powdermixture 1,100 8.16 11.47 71.1 when cumulative number of ball millrevolutions was 1,810,080

The relative density of the sintered product was low, i.e., 71.1%, sothat the sintered product contained a large amount of voids. If therelative density is computed using the theoretical density computed inconsideration of a reduction in the amount of carbon during sintering,the relative density in Comparative Example 1 may be much smaller than71.1%.

Example 4

In Examples 1 to 3 and Comparative Example 1, the metal components areFe and Pt forming a binary system. Whereas, in Example 4, the metalcomponents are Fe, Pt, and Cu forming a ternary system.

The target compositions of a powder mixture and a target in Example 4are 66.6(45Fe-45Pt-10Cu)-33.4C. More specifically, the targetcomposition of the metal components is 45 at % Fe-45 at % Pt-10 at % Cu,and the target compositional ratios of the FePtCu alloy and C (carbon)are 66.6 at % for the FePtCu alloy and 33.4 at % for C. In Example 4,the content of C is smaller than that in Examples 1 to 3 and ComparativeExample 1. However, as described later, since part of C (carbon) isvolatilized during production of the powder mixture and during sinteringof the target, the compositional ratios of the FePtCu alloy and C(carbon) in the powder mixture and target obtained slightly deviate fromthe target values. When the content of C (carbon) is represented not byat % but by vol %, the target compositions of the powder mixture andtarget in Example 4 are (45Fe-45Pt-10Cu)-25 vol % C.

In Example 4, as in Example 3, the mixing container was filled with agas mixture (Ar-20% O₂) and then sealed, and FePtCu powder and the Cpowder were mixed in the sealed mixing container. However, thecumulative number of ball mill revolutions was different from that inExample 3, and the number of times and the timing of introduction offresh air by opening the mixing container during mixing were differentfrom those in Example 3. Another difference from Example 3 was that thesintering temperature during production of the sintered product was1,350° C.

A powder mixture and a sintered product were produced in the same manneras in Example 3 except for the above differences.

When the cumulative number of ball mill revolutions reached 935,280,1,870,560, 2,805,840, 4,073,760, and 5,674,320, the mixing container wasopened, and whether or not ignition had occurred was visually checked.However, no ignition was found at each point.

Powder mixtures mixed until the cumulative number of ball millrevolutions reached 4,073,760 and 5,674,320 were subjected to hotpressing under the conditions of temperature: 1,350° C., pressure: 26.2MPa, time: 45 min., atmosphere: a vacuum of 5×10⁻² Pa or lower tothereby produce sintered products.

The density of each of the produced sintered products was measured bythe Archimedes method, and the measured value was divided by atheoretical density to determine the relative density. The results areshown in TABLE 10 below. The content of carbon in each sintered productshown in TABLE 11 was used as the amount of carbon used to compute thetheoretical density, that is to say, the theoretical density wascomputed in consideration of a reduction in the amount of carbon duringmixing and sintering.

TABLE 10 Sintering Theoretical Relative Sintered powder temperatureDensity density density mixture (° C.) (g/cm³) (g/cm³) (%) Powdermixture 1,350 10.82 11.75 92.1 when cumulative number of ball millrevolutions was 4,073,760 Powder mixture 1,350 11.33 11.75 96.4 whencumulative number of ball mill revolutions was 5,674,320

The relative densities of the two sintered products were high, i.e.,92.1% and 96.4%, so that the amount of voids in each of the obtainedsintered products was small.

The contents of oxygen and nitrogen in each of the sintered productsmolded by sintering of the powder mixtures shown in TABLE 11 at asintering temperature of 1,350° C. were measured using a TC-600 SeriesNitrogen/Oxygen Determinator manufactured by LECO Corporation, and thecontent of carbon was measured using a Carbon/Sulfur Analyzermanufactured by HORIBA, Ltd. The measurement results are shown in TABLE11 below.

TABLE 11 Oxygen Nitrogen Carbon Sintered powder mixture (mass %) (massppm) (mass %) Powder mixture when 536 — 4.00 cumulative number of ballmill revolutions was 4,073,760 Powder mixture when 293 — 3.83 cumulativenumber of ball mill revolutions was 5,674,320

As shown in TABLE 11, the contents of oxygen in the sintered productswere very small.

The structure of the obtained sintered product was observed under ascanning electron microscope (SEM). FIGS. 10, 11, and 12 show SEMphotographs of the sintered product. FIG. 10 is an SEM photograph at alow magnification (an image taken at a magnification of 3,000×) (a barscale in the photograph represents 1 μm). FIG. 11 is an SEM photographat a medium magnification (an image taken at a magnification of 5,000×)(a bar scale in the photograph represents 1 μm), and FIG. 12 is an SEMphotograph at a high magnification (an image taken at a magnification of10,000×) (a bar scale in the photograph represents 1 μm). In FIGS. 10,11, and 12, black regions are the C phase, and white regions are theFePt alloy phase. As can be seen from FIGS. 10, 11, and 12, fine regionsof the C phase are dispersed in the entire area of the structure.

Next, the size of the phase in the obtained sintered product (thecumulative number of ball mill revolutions: 5,674,320, sinteringtemperature: 1,350° C.) was determined by the intercept method.

Specifically, a total of five lines were drawn on the SEM photograph ofthe cross section of the target in FIG. 12 (an image taken at amagnification of 10,000×). More specifically, two horizontal lines weredrawn on the SEM photograph of FIG. 12 in a left-right direction suchthat the image was divided vertically into thirds, and three verticallines were drawn in a vertical direction such that the image was dividedhorizontally into quarters.

For each of the five lines, the total length of line segmentsintersecting the C phase and the number of the C phase intersected bythe line were determined. Then the average of the lengths of thesegments of the five lines that intersected the C phase was determined(by dividing the total length of the line segments intersecting the Cphase by the number of the C phases intersected by the lines), and theobtained value was used as the average size of the C phase determined bythe intercept method. The results showed that the average size of the Cphase determined by the intercept method was 0.25 μm.

(Discussion)

The principal experimental data in Examples 1 to 4 and ComparativeExample 1 is summarized in TABLE 12 below.

TABLE 12 Cumulative number of Average Target C Atmosphere ball millSintering Relative size of Type of content during revolutionstemperature density C phase alloy (at %) mixing (Number) (° C.) (%)Ignition (μm) Example 1 FePt 60 Circulating air 4,136,400 1,460 96.4 NO0.52 Example 2 FePt 60 Sealed air 2,805,840 1,380 93.4 NO — 4,073,7601,340 92.0 NO 0.50 Example 3 FePt 40 Ar + O₂ 1,810,080 1,300 100 NO —3,181,680 1,250 96.9 NO — 3,181,680 1,300 95.2 NO 0.33 Comparative FePt40 Ar 1,405,080 1,100 71.1 NO — example 1 2,816,640 — — YES — Example 4FePtCu 33.4 Ar + O₂ 5,674,320 1,350 96.4 NO 0.25

In Examples 1 to 3, the entire process for mixing the FePt powder andthe C powder was performed in an atmosphere containing oxygen. InExample 4, the entire process for mixing the FePtCu powder and the Cpowder was performed in an atmosphere containing oxygen. In Example 1,no ignition was found even after the cumulative number of ball millrevolutions reached 4,136,400. In Example 2, no ignition was found evenafter the cumulative number of ball mill revolutions reached 4,073,760.In Example 3, no ignition was found even after the cumulative number ofball mill revolutions reached 3,181,680. In Example 4, no ignition wasfound even after the cumulative number of ball mill revolutions reached5,674,320.

Whereas, in Comparative Example 1 in which the FePt powder and the Cpowder were mixed in an argon atmosphere containing no oxygen during aperiod from when the cumulative number of ball mill revolutions was209,521 to when it reached 2,816,640, ignition was found when the mixingcontainer was opened at the point of time when the cumulative number ofball mill revolutions was 2,816,640.

In Examples 1 to 4, the sintered products were produced using powdermixtures mixed until the cumulative number of ball mill revolutionsexceeded 2,800,000, and the relative density of each of the producedsintered products was 92% or higher. Whereas, in Comparative Example 1,the sintered product was produced using the powder mixture mixed untilthe cumulative number of ball mill revolutions reached 1,405,080, andthe relative density of the produced sintered product was small, i.e.,71.1%. One reason for this may be the influence of low sinteringtemperature, 1,100° C., in Comparative Example 1. Another reason may bethat, since the cumulative number of ball mill revolutions was small,the particle diameter of the C powder in the powder mixture used toproduce the sintered product was not sufficiently reduced, so that voidsin the sintered product became large and the relative density of thesintered product became small.

In Examples 1, 2, 3, and 4, the sizes of the C phase in the obtainedtargets were measured by the intercept method. The sizes of the C phasewere smaller than 0.6 μm, i.e., 0.52 μm, 0.50 μm, 0.33 μm, and 0.25 μm,respectively, and were found to be sufficiently reduced.

The size of the C phase in the obtained target was 0.52 μm and 0.50 μmin Examples 1 and 2 in which the content of C in the target was 60 at %,0.33 μm in Example 3 in which the content of C in the target was 40 at%, and 0.25 μm in Example 4 in which the content of C in the target was33.4 at %. The size of the C phase decreases as the content of Cdecreases. This may be because, when the content of C is large, regionsof the C phase are easily connected, so that the size of the C phase isless likely to decrease.

INDUSTRIAL APPLICABILITY

The target according to the present invention can be preferably used asan FePt—C-based sputtering target. The production process according tothe present invention can be preferably used as a process for producingan FePt—C-based sputtering target.

What is claimed is:
 1. A process for producing an FePt—C-basedsputtering target, comprising: adding C powder containing unavoidableimpurities to FePt-based alloy powder containing Pt in an amount of 40at % or more and 60 at % or less with the balance being Fe andunavoidable impurities; mixing the C powder and the FePt-based alloypowder in an atmosphere containing oxygen to produce a powder mixture;and then molding the produced powder mixture while the powder mixture isheated under pressure.
 2. The process for producing an FePt—C-basedsputtering target according to claim 1, wherein the C powder is addedsuch that C is contained in an amount of 21 at % or more and 70 at % orless based on the total amount of the powder mixture.
 3. The process forproducing an FePt—C-based sputtering target according to claim 1,wherein oxygen is supplied to the atmosphere from outside of theatmosphere.
 4. The process for producing an FePt—C-based sputteringtarget according to claim 3, wherein the oxygen is supplied by supplyingair.
 5. The process for producing an FePt—C-based sputtering targetaccording to claim 1, wherein the atmosphere is air.
 6. The process forproducing an FePt—C-based sputtering target according to claim 1,wherein the atmosphere is composed substantially of an inert gas andoxygen.
 7. The process for producing an FePt—C-based sputtering targetaccording to claim 1, wherein a concentration of oxygen in theatmosphere is 10 vol % or higher and 30 vol % or lower.
 8. The processfor producing an FePt—C-based sputtering target according to claim 1,wherein the atmosphere is released to air during the mixing.
 9. Theprocess for producing an FePt—C-based sputtering target according toclaim 1, wherein a C phase in the obtained FePt—C-based sputteringtarget has an average phase size of 0.6 μm or less as determined by anintercept method.
 10. The process for producing an FePt—C-basedsputtering target according to claim 1, wherein an atmosphere when thepowder mixture is molded while heated under pressure is a vacuum or aninert gas atmosphere.
 11. The process for producing an FePt—C-basedsputtering target according to claim 1, wherein oxygen in the obtainedFePt—C-based sputtering target is contained in an amount of 100 mass ppmor less.
 12. The process for producing an FePt—C-based sputtering targetaccording to claim 1, wherein nitrogen in the obtained FePt—C-basedsputtering target is contained in an amount of 30 mass ppm or less. 13.The process for producing an FePt—C-based sputtering target according toclaim 1, wherein the FePt-based alloy powder is produced by an atomizingmethod.
 14. The process for producing an FePt—C-based sputtering targetaccording to claim 13, wherein the atomizing method is performed usingargon gas or nitrogen gas.
 15. The process for producing an FePt—C-basedsputtering target according to claim 1, wherein the obtainedFePt—C-based sputtering target is used for a magnetic recording medium.16. A process for producing an FePt—C-based sputtering target,comprising: adding C powder containing unavoidable impurities toFePt-based alloy powder containing Pt in an amount of 40 at % or moreand less than 60 at % and one or more kinds of metal elements other thanFe and Pt in an amount of more than 0 at % and 20 at % or less with thebalance being Fe and unavoidable impurities and with the total amount ofPt and the one or more kinds of metal elements being 60 at % or less;mixing the C powder and the FePt-based alloy powder in an atmospherecontaining oxygen to produce a powder mixture; and then molding theproduced powder mixture while the powder mixture is heated underpressure.
 17. The process for producing an FePt—C-based sputteringtarget according to claim 16, wherein the one or more kinds of metalelements other than Fe and Pt are one or more kinds of Cu, Ag, Mn, Ni,Co, Pd, Cr, V, and B.
 18. The process for producing an FePt—C-basedsputtering target according to claim 16, wherein the one or more kindsof metal elements other than Fe and Pt include Cu.
 19. The process forproducing an FePt—C-based sputtering target according to claim 16,wherein the one or more kinds of metal elements other than Fe and Pt areonly Cu.
 20. The process for producing an FePt—C-based sputtering targetaccording to claim 16, wherein the C powder is added such that C iscontained in an amount of 21 at % or more and 70 at % or less based onthe total amount of the powder mixture.
 21. The process for producing anFePt—C-based sputtering target according to claim 16, wherein oxygen issupplied to the atmosphere from outside of the atmosphere.
 22. Theprocess for producing an FePt—C-based sputtering target according toclaim 21, wherein the oxygen is supplied by supplying air.
 23. Theprocess for producing an FePt—C-based sputtering target according toclaim 16, wherein the atmosphere is air.
 24. The process for producingan FePt—C-based sputtering target according to claim 16, wherein theatmosphere is composed substantially of an inert gas and oxygen.
 25. Theprocess for producing an FePt—C-based sputtering target according toclaim 16, wherein a concentration of oxygen in the atmosphere is 10 vol% or higher and 30 vol % or lower.
 26. The process for producing anFePt—C-based sputtering target according to claim 16, wherein theatmosphere is released to air during the mixing.
 27. The process forproducing an FePt—C-based sputtering target according to claim 16,wherein a C phase in the obtained FePt—C-based sputtering target has anaverage phase size of 0.6 μm or less as determined by an interceptmethod.
 28. The process for producing an FePt—C-based sputtering targetaccording to claim 16, wherein an atmosphere when the powder mixture ismolded while heated under pressure is a vacuum or an inert gasatmosphere.
 29. The process for producing an FePt—C-based sputteringtarget according to claim 16, wherein oxygen in the obtainedFePt—C-based sputtering target is contained in an amount of 100 mass ppmor less.
 30. The process for producing an FePt—C-based sputtering targetaccording to claim 16, wherein nitrogen in the obtained FePt—C-basedsputtering target is contained in an amount of 30 mass ppm or less. 31.The process for producing an FePt—C-based sputtering target according toclaim 16, wherein the FePt-based alloy powder is produced by anatomizing method.
 32. The process for producing an FePt—C-basedsputtering target according to claim 31, wherein the atomizing method isperformed using argon gas or nitrogen gas.
 33. The process for producingan FePt—C-based sputtering target according to claim 16, wherein theobtained FePt—C-based sputtering target is used for a magnetic recordingmedium.